I don't think you can easily buy one way tickets ex-NRT in China. I am getting Tokyo consolidator prices on the order of Y44,800 for May (after Golden week) through mid-June for a round trip NRT-Shanghai, this is on the dialy Northwest nonstop (Y5,000 more for each flight on a Sunday). Probably, unfortunately, one way isn't much cheaper than the round trip, but this round trip fare is actually a little bit lower than $454.